Frozen product machines, such as frozen carbonated beverage (FCB) machines, utilize a freeze cylinder or barrel for producing a slush beverage or frozen food product. An evaporator coil of a refrigeration system is heat exchange coupled with the freeze barrel for cooling and freezing liquid product delivered into the barrel. A beater bar and scraper assembly is rotated in the barrel to scrape thin iced or frozen layers of the frozen product from the inner surface of the barrel for dispensing to customers. The freeze barrel is periodically defrosted by operating the refrigeration system in a defrost cycle to heat the evaporator coil and thereby warm and melt product in the barrel. A defrost schedule may be manually programmed into the machine, so that defrost cycles occur automatically according to scheduled time periods. A defrost cycle may also be initiated manually should ice particles be viewed in the dispensed beverage product and defrosting deemed necessary.
Frozen product machines often utilize two or more freeze barrels to accommodate service from a single machine of more than one product, such as more than one flavor of frozen beverage. A frozen product machine with a plurality of freeze barrels usually has a single refrigeration system, with an outlet from a compressor coupled through each of a plurality of adjustable expansion valves to inlets to associated ones of a plurality of evaporator coils, with each evaporator coil being heat exchange coupled to an associated one of the freeze barrels. The outlets from the evaporator coils are normally connected together and coupled to a common return to the compressor suction inlet. During defrost of one barrel, the suction pressure on the return side of the refrigeration system rises. Since the barrel evaporator coils have a common outlet, the other barrel(s) will also see a suction pressure rise. This suction pressure rise in other barrel(s) allows the frozen product in them to warm. Given enough time, warming of product in the other barrel(s) causes the product to become unsatisfactory for service to customers.